This invention relates to blends including polymer/clay nanocomposite materials containing a polyolefin polymer, a functionalized or grafted polymer, and an organically modified clay material therein, as well as articles made therefrom and processes for stretching and/or drawing such high melt-strength blends.
Amorphous polymers, such as acrylonitrile-butadiene-styrene (ABS) and polystyrene, are typically used in industrial processes where stretching and/or drawing of the material is required (i.e., thermoforming, melt spinning, blow molding and foaming.) Polyolefins, including polypropylene (PP) and polyethylene (PE), can potentially replace ABS or polystyrene blends in order to manufacture articles, such as automotive parts, electronic components, fibers, household equipment, containers and bottles, packaging material, and construction equipment. The advantages of polyolefins over ABS or polystyrene blends are improved, long-term ultraviolet and heat resistance, reduced fogging, better recyclability, and lower raw material costs.
To be useful in such industrial processes, the polymer material must exhibit sufficient elastic behavior to resist sagging, but remain viscous enough to flow into the mold under stress. One advantage of ABS and polystyrene is that their rubbery elastic state exists over a wider temperature range compared to that of the semi-crystalline polyolefins. Due to their sharp melting point, polyolefins such as polypropylene pass through the viscoelastic plateau very rapidly on heating, resulting in poor melt strength and sag. In thermoforming, for example, deformations in the thermoformed sheet caused by sagging may in turn lead to irregularities in articles made by the process, such as unacceptable variations in weight and thickness, which may even result in tearing of the sheet.
To address the problems associated with thermoforming polyolefins, Japanese Patent Publication No. 51-75761, published in June, 1976, discloses a polypropylene sheet laminated onto a sagging-free sheet of a resin different from polypropylene in attempts to solve the problem of sagging; however, this may be unsuitable for general use since it raises problems as to lamination means, selection of resins used and the like. WO 00/12572 details a long-chain branched polypropylene with high melt strength and good processability formed by contacting propylene monomers in a reactor with an inert hydrocarbon solvent and one or more single site catalysts capable of producing stereospecific propylene at 40-120xc2x0 C. However, the use of this high-melt-strength polypropylene (HMS-PP) gives only limited improvements, since it affects only one component of the polyolefin compound (i.e., polypropylene). It is currently recognized, for example, in Lau et al., Polymer Eng. Sci. 38 (1998), page 1915, that for a material to have good thermoformability, it must exhibit high melt strength.
Nancomposites are a new class of composites that are particle-filled polymers for which at least one dimension of the dispersed particle is in the nanometer range (10xe2x88x929 meter). Because of the size of the dispersed particles, the nanocomposites exhibit modified mechanical, thermal and optical properties as compared to pure polymers or conventional composites.
The most commonly used and investigated types of polymer nanocomposites are those based on clays and layered silicates. The nanocomposites are obtained by the intercalation or penetration of the polymer (or a monomer subsequently polymerized) inside the galleries of layered clay material and the subsequent exfoliation or dispersion of the intercalate throughout the final polymer blend. To be more compatible with organic polymers, the layered clay material is usually modified by an ion exchange process with cationic surfactants, such as alkylammonium or alkylphosphonium ions.
The great difficulty when using clay in a polyolefin matrix is the opposing nature of the materials. The polymeric portion of the matrix is usually a nonpolar organic material, whereas the clay is a much more polar inorganic material. This incompatibility hinders the direct intercalation or exfoliation of the clay in the final polymer blend. See, for example, Alexandre et al., Mater. Sci. Eng. Rpts. 28 (2000), page 1. To introduce favorable interactions between the polymer and the layered clay material, a functionalized polyolefin such as a maleic-anhydride-modified polypropylene must be added to the composite. This method has been reported in Kawasumi et al., Macromolecules 30 (1997), page 6333.
Increased interest in developing a polymer/clay nanocomposite to improve the stiffness/impact balance of polyolefins has been reported. See, for example, Hasegawa et al., J. App. Pol. Sci. 67 (1998), page 87. No applications have been commercialized at the present time, however, presumably as a result of the lack of direct intercalation or exfoliation of the organically modified clay in the polyolefin matrix that renders such materials difficult to prepare.
U.S. Pat. No. 5,552,469 describes the preparation of intercalates derived from certain clays and water soluble polymers, such as polyvinyl alcohol and polyacrylic acid. Although the specification lists a wide range of resins including polyesters and rubbers that can be used in blends with these intercalates, there is no teaching of how to make such blends. Further, the water soluble polymer/clay mixture is taught to be incompatible with hydrophobic polyolefins (i.e., all blends containing polypropylene).
U.S. Pat. No. 5,910,523 describes a process wherein the clay layer is functionalized with an aminosilane and then grafted to a carboxylated or maleated polyolefin through an amine-carboxyl reaction. The use of xylene solvent in this process, however, makes the method cumbersome, environmentally unfriendly, and expensive to commercialize.
U.S. Pat. No. 6,121,361 describes a process wherein a composite clay material is formed of a clay mineral having an interlayer section by first bonding a swelling agent such as an onium ion having 6 or more carbon atoms to the clay mineral via an ionic bond for expanding the interlayer section and rendering the interlayer section compatible with an organic molecule, and then introducing a polymer having a polar group in a main chain and/or a side chain. Degradation of the mechanical properties of the composites, however, can occur whenever excess amounts of the swelling agent precipitates out of solution.
U.S. Pat. No. 6,153,680 discloses a composition useful for automotive interior parts which includes a blend of polypropylene, an uncrosslinked ethylene copolymer, an ionomer, a crosslinking agent and a silicone elastomer. Clay fillers in the nanometer-size range are listed as optional fillers, but there is no teaching that the use of such fillers improves the mechanical properties of the blend and no teaching of the details of any such filled-blends.
Moreover, none of the prior art references described above teaches the surprising discovery of the present invention, i.e., that the addition of polymer/clay nanocomposites to such polyolefins improves the melt strength of the final polymer blend. Thus, there remains a need to develop processes using polyolefins in thermoforming, melt spinning, blow molding, and foaming, and the improved articles resulting from the processes of the invention.
The invention encompasses methods of manufacturing an article by providing a polyolefin/clay nanocomposite masterbatch formed from about 0 to 99 percent by weight of polyolefin, from about 1 to 100 percent by weight of functionalized polyolefin, and from about 10 to 50 percent by weight based on the total masterbatch of an organically modified clay, melt blending from about 1 to 30 percent by weight of the nanocomposite masterbatch and from about 70 to 99 percent by weight of a polyolefin blend to form a final polyolefin blend and to ensure sufficient exfoliation of the organically modified clay into the final polyolefin blend so that the melt strength of the final polyolefin blend is greater than the melt strength of the polyolefin blend before modification with the nanocomposite masterbatch, and forming the article using the final polyolefin blend.
In one embodiment, the masterbatch present in an amount from about 2 to 27 percent by weight and which includes from about 50 to 80 percent by weight of polyolefin, from about 20 to 50 percent by weight of functionalized polyolefin, and from about 20 to 48 percent by weight of organically modified clay, and the polyolefin blend present in an amount from about 73 to 98 percent by weight, are melt blended to form the final polymer blend which has a modified melt strength so that the ratio of the modified melt strength to the melt strength before modification measured at 220xc2x0 C. is at least about 1.5 but no more than about 15. In a preferred embodiment, the masterbatch present in an amount from about 3 to 25 percent by weight and which includes from about 60 to 70 percent by weight of polyolefin, from about 30 to 40 percent by weight of functionalized polyolefin, and from about 30 to 45 percent by weight of organically modified clay wherein the amounts total to 100 percent, and the polyolefin blend present in an amount from about 75 to 97 percent by weight are melt blended to form the final polyolefin blend which has a modified melt strength so that the ratio of the modified melt strength to the melt strength before modification measured at 220xc2x0 C. is at least about 1.6 but no more than about 14 and the final polyolefin blend has a shear viscosity that is at least about 5 times that of the shear viscosity of the polymer blend measured under the same conditions but without the organically modified clay.
The invention also encompasses methods of manufacturing an article which includes a polyolefin/clay nanocomposite blend by forming a final polymer blend. This method includes combining from about 50 to 98 percent by weight of a polyolefin, from about 1 to 20 percent by weight of a functionalized polyolefin, and an organically modified clay in an amount sufficient to provide a modified melt strength, so that a ratio of the modified melt strength to the melt strength before modification measured at 220xc2x0 C. is at least about 1.5 but no more than about 15, and forming the article using the polyolefin/clay nanocomposite blend.
In one embodiment, the polyolefin blend in the article includes from about 70 to 95 percent by weight of polyolefin, from about 1 to 10 percent by weight of functionalized polyolefin, and from about 4 to 20 percent by weight of organically modified clay to provide a ratio of the melt strength of the modified blend to the melt strength of the blend before modification measured at 220xc2x0 C. of at least about 1.6 but no more than about 14. In a preferred embodiment, the polyolefin blend in the article includes from about 85 to 92 percent by weight of polyolefin, from about 2 to 5 percent by weight of functionalized polyolefin, and from about 6 to 10 percent by weight of organically modified clay, wherein the total amoutns to 100%, to provide a ratio of the melt strength of the modified blend to the melt strength of the blend before modification measured at 220xc2x0 C. of at least about 1.6 but no more than about 14.
In either method of forming articles, the forming can include at least one of thermoforming, extrusion, melt spinning, blow molding or foam processing.
The invention also encompasses articles formed from a final polyolefin blend containing a polyolefin/clay nanocomposite masterbatch including from about 0 to 99 percent by weight of polyolefin, from about 1 to 100 percent by weight of a functionalized polyolefin, and from about 10 to 50 percent by weight based on the final polyolefin blend of an organically modified clay, and any optional components, wherein the final polyolefin blend includes from about 1 to 30 percent by weight of the nanocomposite masterbatch and about 70 to 99 percent by weight of a polyolefin blend, and wherein the organoclay is sufficiently exfoliated into the polyolefin blend to provide the final polyolefin blend with a modified melt strength so that the ratio of the modified melt strength to the melt strength before modification measured at 220xc2x0 C. is at least about 1.5 but no more than about 15.
In one embodiment, the masterbatch is present in an amount from about 2 to 27 percent by weight and includes from about 50 to 80 percent by weight of polyolefin, from about 20 to 50 percent by weight of functionalized polyolefin, and from about 20 to 48 percent by weight of organically modified clay, and the polyolefin blend is present in an amount from about 73 to 98 percent by weight, to form the final polymer blend which has a modified melt strength so that the ratio of the modified melt strength to the melt strength before modification measured at 220xc2x0 C. is at least about 1.5 but no more than about 15. In a preferred embodiment, the masterbatch is present in an amount from about 3 to 25 percent by weight and includes from about 60 to 70 percent by weight of polyolefin, from about 30 to 40 percent by weight of functionalized polyolefin, and from about 30 to 45 percent by weight of organically modified clay, and the polyolefin blend is present in an amount from about 75 to 97 percent by weight, to form the final polyolefin blend which has a modified melt strength so that the ratio of the modified melt strength to the melt strength before modification measured at 220xc2x0 C. is at least about 1.6 but no more than about 14 and the final polyolefin blend has a shear viscosity that is at least about 5 times that of the shear viscosity of the polymer blend measured under the same conditions but without the organically modified clay.
In one embodiment, the functionalized polyolefin includes a homopolymer, copolymer, and/or mixture of ethylene and/or propylene, wherein a functional monomer with a pendant reactive polar group is grafted onto the polyolefin. In another alternative or additional embodiment, the nanocomposite-modified polyolefin blend further includes one or more optional additive components including nucleating agents, fillers, plasticizers, impact modifiers, colorants, mold release agents, lubricants, antistatic agents, pigments, fire retardants, and ultraviolet stabilizers, or mixtures thereof. The addition of the nanocomposite masterbatch provides a range of temperatures for forming the article that is at least about 10xc2x0 C. greater than without the inclusion of a sufficient amount of the clay nanocomposite.
The invention also encompasses articles formed from a modified polyolefin blend including from about 50 to 98 percent by weight of polyolefin, from about 1 to 20 percent by weight of functionalized polyolefin, and from about 1 to 30 percent by weight of organically modified clay that is sufficiently dispersed in the polyolefin and functionalized polyolefin to provide a modified melt strength that is greater than the melt strength of the blend before modification.
In one embodiment, the polyolefin blend includes from about 70 to 95 percent by weight of polyolefin, from about 1 to 10 percent by weight of functionalized polyolefin, and from about 4 to 20 percent by weight of organically modified clay. In a preferred embodiment, the polyolefin blend includes about 85 to 92 percent by weight of polyolefin, from about 2 to 5 percent by weight of functionalized polyolefin, and from about 6 to 10 percent by weight of organically modified clay. In one embodiment, the polyolefin blend has a ratio of the melt strength of the modified blend to the melt strength of the blend before modification measured at 220xc2x0 C. of at least about 1.5 but no more than about 15. In a preferred embodiment, the polyolefin blend has a ratio of the melt strength of the modified blend to the melt strength of the blend before modification measured at 220xc2x0 C. of at least about 1.6 but no more than about 14.
The organically modified clay preferably includes a reaction product of at least one organoclay and at least one swelling agent. The swelling agent can include at least one of cationic surfactants; amphoteric surface active agents; derivatives of aliphatic, aromatic or arylaliphatic amines, phosphines and sulfides; organosilane compounds; protonated amino acids and salts thereof; and combinations thereof.
The invention also encompasses an automotive component, a building material, a packaging material, an electrical material, or a nonwoven fabric or fiber formed from the articles described above.